I, for one, will never buy another chain-drive bike again. Its the reason I chose the ST over a DL1000. On my last big ride on my KLR, the relatively new chain (high quality O-ring, properly lubed & adjusted...aprox. 2k miles on it) decided to grenade at aprox. 80 mph in Virginia. When i say grenade, I don't mean cleanly break and spit out on the road like most breaks. This one wrapped itself around the rear hub and flung the free end like a whip at 80 mph. The resulting carnage consisted of almost 3 hours downtime sourcing a replacement, $1500+ in total damage including gouged engine case, swingarm, shredded airbox, rim & rear hub, and pannier rack. I'm just glad the wheel didn't lock up with the truck that was right behind me!
Chains are archaic and outdated. There is no need for them on most adventure bikes, with the long travel shafts are capable of, and they are MUCH more reliable than chains (yes, even BMWs).
I realize chain problems aren't common, but shaft problems are even less common. My wife is in the market for a bike, and after seeing the damage to my KLR, she won't even consider a chain drive bike. The DL650 was a possible candidate, but the chain drive kills it.
Is my fear irrational? Yes, possibly. But being the one sitting on the side of the highway pulling broken pieces off my bike, thankful I didn't end up as road pizza, I think I'm entitled to be a little irrational.